The present invention relates to a control assembly for exhaust timing control. In particular, the present invention relates to a control assembly for controlling the effective height of an exhaust port of a cylinder of a two-cycle internal combustion engine.
Various arrangements for controlling exhaust timing are known. For example, U.S. Pat. No. 4,121,552, entitled xe2x80x9cExhaust Means For Two Cycle Enginesxe2x80x9d to Mithuo et al. and U.S. Pat. No. 4,333,431, entitled xe2x80x9cWater-Cooled Two Stroke Engine Having Exhaust Port Timing Control Valve Meansxe2x80x9d to Iio et al. disclose arrangements for controlling exhaust timing. These arrangements increase engine torque particularly in lower and middle r.p.m. ranges. Additional control arrangements are disclosed in AT 369 866 B, which corresponds to U.S. Pat. No. 4,399,788, entitled xe2x80x9cInternal Combustion Engine Comprising Means for Controlling The Axial Extent of An Exhaust Port in a Cylinderxe2x80x9d to Bostelmann, and U.S. Pat. No. 4,364,346, entitled xe2x80x9cExhaust Timing Control Device for a Two-Cycle Enginexe2x80x9d to Shiohara. These arrangements include a plate-shaped control valve assembly that is shiftable in position relative to the exhaust port by a pressurized membrane, which acts as an adjustment assembly. In an advanced position, the control valve assembly exposes only a portion of the exhaust port of the cylinder. In a retracted position, the exhaust port is fully exposed. Exhaust gas pressure or overpressure in the crankcase is used to operate the pressurized membrane.
Over the years, these arrangements have to be proven successful when used in connection with carburetor engines. When used in two-cycle engines with fuel injection, in particular with direct injection, however, numerous problems exist. Due to the incomplete combustion of fuel particles and additionally effective crack processes, oil carbon or soot-like deposits form on the surface of the control valve assembly. These deposits also form on the walls of the guide. These deposits can have a lasting detrimental effect on the function of the slide valve. In particular, the axial movement of the slide valve is inhibited, which can reduce engine performance.
It is an object of the present invention to provide a control assembly for exhaust timing control that eliminates the problems identified in the above-identified prior art.
It is another object of the present invention to provide a control assembly for exhaust timing control having a sealing arrangement that protects the control assembly from deposits of incompletely burnt fuel particles and the like to provide undisturbed long-term operation.
It is another object of the present invention to provide a control assembly that is pneumatically operated for improved operating performance.
It is another object of the present invention to provide a control assembly having means for removing y particles that may form on the control valve assembly during operation.
The foregoing and other objects, features, characteristics and advantages of the present invention as well as the methods of operation and functions of the related elements of structure, and the combination of parts and economies of manufacture, will be apparent from the following detailed description and the appended claims, taken in connection with the accompanying drawings, all of which form a part of the specification.
In response to the foregoing challenges, applicants have developed an innovative control assembly for exhaust timing control. The present invention is directed to a control assembly for exhaust timing control in a two-cycle internal combustion engine. The two-cycle internal combustion engine includes a housing and has at least one cylinder. Each cylinder has an exhaust port with an effective height, which is in communication with an exhaust channel. In accordance with the present invention, the control assembly includes a control valve assembly for modifying the effective height of the exhaust port, a guide channel formed in the housing, an operating assembly for moving the control valve assembly within guide channel between a retracted position and an extended position, and a sealing arrangement between the control valve assembly and the guide channel.
In accordance with the present invention, the guide channel is formed in the housing of the internal combustion engine. When the control valve assembly is in the extended position, the effective height of the exhaust port is reduced. The control valve assembly extends into the exhaust channel adjacent the exhaust port when in the extended position.
In accordance with the present invention, the sealing arrangement is located on at least one of the control valve assembly and the guide channel. The sealing arrangement may include a chamfer formed in the control valve assembly and a complementary chamfer formed in at least a portion of the guide channel. The chamfer being adapted to sealingly engage the complementary chamfer when the control valve assembly is in the extended position. The sealing arrangement may further include a first sealing surface on the control valve assembly, and a second sealing surface on he guide channel opposite the first sealing surface. The first sealing surface is adapted to be pressed against the second sealing surface when the chamfer contacts the complementary chamfer. The operating assembly may supply the necessary force to press the first sealing surface against the second sealing surface. In this particularly advantageous arrangement, the chamfer is present on one side of the guide channel. The control valve assembly, in the extended position being sealingly pressed against the opposite wall of the guide channel. With this configuration, not only the sealing against penetration of solid particles is achieved, but improved heat conduction away from the control valve assembly becomes possible.
The sealing arrangement may include at least one gasket located on the control valve assembly. The sealing arrangement may include an area of contact between the control valve assembly and the guide channel. It is contemplated that the above-described sealing arrangements may be used alone or in combination.
The sealing arrangement is positioned to be effective between the guide channel and the control valve assembly in an end region of the control valve facing the exhaust port. With such an arrangement, a penetration of depositing particles between control valve assembly and guide channel, primarily in the advanced position of the control valve assembly, in which particularly large amounts of such particles would deposit, can be prevented in a simple, yet efficient manner.
In accordance with the present invention, at least one stop may be provided to limit the axial movement of the control valve assembly. A first stop may limit the movement of the control valve assembly to the retracted position. A second stop may limit the movement of the control valve assembly to the extended position.
To effect additional sealing of the control valve assembly in the guide channel relative to exhaust gas admixed with incompletely burnt depositing particles flowing in from the exhaust port, and to additionally define the advanced position of the control valve assembly, it is furthermore advantageous if the control valve assembly has an enlarged cross-sectional portion at a distance from its end facing the exhaust port, this enlarged cross-sectional portion abutting against a separate stop of the guide in the advanced position of the control valve assembly.
In accordance with the present invention, the operating assembly includes a spring assembly for biasing the control valve assembly into the extended position. The operating assembly may further include a selectively operable piston assembly for moving the control valve assembly from the extended position to the retracted position against the bias of the spring assembly, a selectively operable supply of compressed air for operating the piston assembly, and an engine management system for selectively operating the supply of compressed air. Since additional resisting forces occur as a consequence of scraping off of deposits and the frictional forces caused due to the seal between the control valve assembly and the guide channel, it is advantageous that the control valve assembly be pneumatically actuated by compressed air from a combustion air compressor.